Technologies, which accurately grasp the amount of air taken into a combustion chamber of an internal combustion engine (this amount of air will hereinafter be referred to simply as “intake air amount”) to control the internal combustion engine appropriately, have been widely known. It is difficult, however, to detect the intake air amount directly. Thus, a method, which detects the flow rate of air in an intake system of the internal combustion engine by means of an air flow sensor and estimates an intake air amount based on the results of detection, is in general use.
In an internal combustion engine having connected thereto an intake system equipped, from upstream to downstream, with a supercharger, an intercooler, a throttle valve, and an intake manifold, for example, the intake air amount is calculated during non-supercharging and during supercharging. With such an intake system, the amount of air on a side upstream of the throttle valve changes according to a change in a boost pressure by the supercharger. Thus, the amount of air found by the air flow sensor is corrected based on the volume of a supercharged chamber upstream of the throttle valve (see, for example, Patent Document 1).
The intake air amount is required to be detected or estimated with a higher accuracy, but it is hard to say that the technology described in Patent Document 1 is fully accurate.
Depending on operating situations, moreover, air may flow reversely from the supercharger toward its upstream side. In this case, the air flow sensor installed upstream of the supercharger poses the problems of detecting the amount of air excessively and lowering the accuracy of the estimated value of the intake air amount based on the excessive air amount.